Method and device for filtering the recycled atmosphere of a print head

ABSTRACT

A device for recovery of the atmosphere containing solvent vapors from at least one ink recovery reservoir of a print machine comprising: n (n≥1) filter(s) arranged at the outlet from at least one ink reservoir (10). Each filter comprises an inlet face, an outlet face, a filter body between the two faces, and conduit(s) for recovering at least part of a liquid condensed on the surface of the inlet face before this liquid has passed through it. Each filter is either: upstream from a condenser, an atmosphere output from the reservoir, passing through the inlet face, and then the filter body and the outlet face before being sent to the condenser; or downstream from the condenser, an atmosphere from the condenser passing through the inlet face, and then the filter body and the outlet face before being sent to at least one print head of the print machine, respectively.

TECHNICAL DOMAIN AND PRIOR ART

The invention relates to print machines, for example continuous inkjetprinters, and particularly but not exclusively to binary continuous jetprinters provided with a multi-nozzle drop generator. It is aimedparticularly at improving an ink and solvent recovery circuit for theseprinters.

Continuous jet printers comprise:

-   -   an ink drop generator,    -   means of separating trajectories of drops generated by the        generator and directing them towards a printing support or to a        catcher.

FIG. 1 show the main modules in an inkjet printer. In a known manner,the printer comprises a console 300, a compartment 400 containing inparticular ink and solvent conditioning circuits, and reservoirs for theink and solvents. In general, the compartment 400 is in the lower partof the console. The top part of the console comprises the control andinstrumentation electronics and display means. The console ishydraulically and electrically connected to a print head 1 through anumbilical 200. A portal frame not shown is used to install the printhead facing a print support 800. The print support 800 moves along adirection represented by an arrow. This direction is perpendicular to analignment axis of the nozzles.

The drop generator comprises nozzles aligned on a nozzle plate along anozzle alignment axis X. During printing, these nozzles eject inkjetscontinuously in a direction Z perpendicular to the nozzle plate.Continuous jet printers include deviated jet printers and binarycontinuous jet printers. Drops formed in deviated continuous jetprinters from a nozzle during the time taken to print a position on aprint support may or may not be deviated. For each print position andfor each nozzle, a segment perpendicular to the movement direction ofthe print support is printed. Deviated drops are deviated such that theywill strike the print support on the required part of the printedsegment, considering the motif to be printed. Undeviated drops arerecovered in a catcher. Deviated continuous jet printers usuallycomprise few ejection nozzles, but each nozzle can print several pixelsdistributed on the print segment for each print position on the support,depending on the motif to be printed.

In binary continuous jet printers, ink from a nozzle only prints onepixel for each print position. The pixel considered does not receive anydrops or receives one or several drops as a function of the motif to beprinted. Consequently, for a high printing speed, the nozzle platecomprises a large number of nozzles, for example 64, to enablesimultaneous printing of one pixel for each nozzle. Drops that are notrequired for printing are recovered in a gutter or catcher. Suchprinters and continuous jet print heads have been extensively described.

A general structure of a print head for a binary continuous jet printeris described below with reference to FIG. 2.

The head shown includes a drop generator 11. An integer number n ofnozzles 4 are aligned on a nozzle plate 2 along an X axis, between afirst nozzle 4 ₁ and a last nozzle 4 _(n).

The first and the last nozzles (4 ₁, 4 _(n)) are the nozzles with thegreatest distance between them.

Each nozzle has a jet emission axis parallel to a Z direction or axis(located in the plane of FIG. 2), perpendicular to the nozzle plate andto the X axis mentioned above. A third axis, Y, is perpendicular to eachof the X and Z axes, the two X and Z axes extending in the plane of FIG.2.

Each nozzle is in hydraulic communication with a pressurized stimulationchamber. The drop generator comprises one stimulation chamber for eachnozzle. Each chamber is provided with an actuator, for example apiezo-electric crystal. An example design of a stimulation chamber isdescribed in document U.S. Pat. No. 7,192,121.

There are sort means or a sort module 600 downstream from the nozzleplate, that will be used to separate drops used for printing from dropsor jet segments not used for printing. FIG. 4 shows a trajectory a ofink drops passing through a slit 17, and a trajectory b of ink dropsdirected towards a gutter 7.

More precisely, drops or jet segments emitted by a nozzle and that willbe used for printing follow a trajectory a along the Z axis of thenozzle, and then strike a print support 8, after having passed throughthe outlet slit 17 (shown in dashed lines in FIG. 2). The slit is opento the outside of the cavity and ink drops to be printed exit throughit; it is parallel to the X direction of nozzle alignment, the Zdirection axes of the nozzles passing through this slit, that is on theface opposite the nozzle plate 2. Its length is equal to at least thedistance between the first and the last nozzle.

Drops or jet segments emitted by a nozzle and not intended for printing,are deviated by means 6 (they follow a trajectory such as trajectory b)and are recovered in a catcher 7 and then recycled. The length of thecatcher along the X direction is equal to at least the distance betweenthe first and the last nozzle.

For example, document U.S. Pat. No. 8,540,350 (FR 2 952 851) thatdescribes a method of avoiding crosstalk between jets from nozzlesadjacent to each other, could be referred to particularly forinformation about the formation of jets and breaking the jets to formdrops, and about the deviation of drops. Reference could also be made toprior art described in U.S. Pat. No. 7,192,121 (FR 2 851 495) describingjet breaking positions depending on whether a drop formed by breakingthe jet will or will not strike the print support.

Liquid inks are used in continuous jet printers. These inks contain asolvent in which ink components are dissolved. It is desirable that inkshould dry quickly once it has been deposited on the print support. Thisis why the solvents used are volatile. The most frequently used solventsare methyl ethyl ketone known as “mek”, acetone or alcohols for examplesuch as ethanol. However, there are disadvantages related to the use ofa volatile solvent. Since it is volatile, the solvent escapes from theink in the form of vapours.

Application WO 2012/038520 includes means of overcoming the disadvantageresulting from the presence of solvent vapour around the jets. Apartfrom a first portion of vapour that can condense on the walls of thecavity in which the jets circulate, a second portion exits outside thiscavity through a slit in the cavity through which drops necessary forprinting will pass. This second part is mixed with ambient air that isthus contaminated. This contamination can lead to the refusal of anenvironmental quality label. When the solvent concentration exceeds agiven threshold, air becomes unsuitable for breathing. Finally, if theconcentration rises, the air-solvent mix can be potentially explosive.

Like this invention, the solution disclosed in application WO2012/038520 concerns binary continuous jet printers. A small portion ofink in these printers, of the order of 10%, is directed towards theprint support. This means that a preponderant part of ink emitted by thenozzles is directed towards a gutter. The different jets together form aliquid curtain that is directed towards the gutter. Only a smallproportion of the ink ejected by the nozzles leaves this curtain in theform of drops directed towards the print support. These drops exit fromthe cavity through a slit parallel to the nozzle alignment direction.The length of this slit is slightly greater than the distance separatingthe nozzles with the greatest distance between each other on the nozzleplate. The liquid curtain moves towards the catcher at a velocity V_(J).As a result of viscosity, air around this curtain is entrained in thesame direction as the jets.

Air immediately in contact with the liquid is entrained at a velocityequal to approximately V_(J). As the radial distance from the jetincreases, the air velocity reduces until a limit is reached at whichits velocity is low in comparison with the velocity V_(j). The thicknessof a so-called “boundary layer” is thus the distance between the liquidair boundary and the limit at which air is no longer entrained by theliquid.

But this solution disclosed in application WO 2012/038520 is notsatisfactory and cannot recover a maximum quantity of solvent vapourspresent in the cavity of the print head in which the jets circulate. Italso limits the Schmidt coefficient of the ink used.

It is also unsuitable for high flows, for example of the order ofseveral tens or several hundred liters per hour.

However, high flows lead to higher risks of condensation in the conduitsand in the print head.

Application WO 2013/173200 describes an example of an ink and solventrecovery circuit in which the ink and gases drawn in through a catcherare directed into a pressurised ink reservoir in which ink is depositedby gravity.

Once again, this solution is not satisfactory and cannot recover amaximum amount of solvent vapours present in the cavity of the printhead inside which the jets circulate and is also unsuitable for highflows, for example of the order of several tens or several hundreds ofliters per hour.

PRESENTATION OF THE INVENTION

Therefore ink flows involved in the case of a multi-jet print head arevery high, and the inventors estimate that 70% of losses in vapour formoriginate from the head and 30% from the umbilical/ink circuit pair. Ifthe source of losses in the head is stopped due to any mechanismwhatsoever, we cannot conclude that the evaporation will be reduced by70% because the equilibrium will be modified and losses in the inkcircuit will be increased.

One solution would consist of:

-   -   completely purifying the flow by extracting solvent vapours and        particles before release into the environment,    -   and supplying air drawn in from outside the head to the jet        curtain.

But purification would be very energy consuming, particularly underextreme environment conditions (ambient temperature up to 45° C.).Moreover, the fresh air supply would be conducive to evaporation andwould lead to accumulative condensates of water vapour originating fromair surrounding the head, inside the system (particularly for a relativehumidity of 90% coupled with an ambient temperature of 45° C.).

Therefore one problem that arises is to treat and recycle the flow inthe recovery line. This could minimise the amount of the treatment.Indeed:

-   -   the desaturation level can then be limited so that no        condensation is created in the return line to the head;    -   the need to draw in outside air is reduced, since most of the        air flow entrained by the jets is derived from recycling; air        renewal is thus reduced and consequently the increase of the        water content in the system will take place more slowly.

Therefore an attempt is made to create a (quasi-)closed loop by drawingin the entire air flow entrained by the jet curtain and returning it tothe print head.

Nevertheless, the volume in the print head communicates with theexterior through the print slit. Considering the fast dynamics imposedby the jet curtain, it seems to be too demanding, for the physicalparameters, to guarantee that there will be zero exchange between theprint head and the external environment. This exchange will directlycontrol the potential to reduce solvent consumption and the increasedconcentration of water in the ink; exchange of air with the exteriorthrough the jet outlet orifice means that gas containing solvent vapourescapes; external gas is drawn into the system to compensate for thelost flow, and this intake will introduce humidity.

However, if well chosen physico-hydraulic parameters would enable such aself-circulation situation in this space, pollution would accumulate dueto the diffusion of ink particles through the liquid/gas interface.Moreover, the ink circuit is also a source of generation of liquid andsolid aerosols due to circulation in a closed space with air in contactwith the ink, at a velocity of a few m/s.

The mechanism for generation of aerosols (firstly ink particles(colorant coated with resin, all in a solvent), and secondly solventdrops without dry extract) can be mechanical and thermodynamic, andthere can be various sources:

-   -   the formation of jets in which the projection of an ink jet        through the nozzle induces strong acceleration (by the        relaxation effect) at its interface and generates particles;    -   splashes due to impact of the jet or drops either with a solid        body or in a two-phase flow;    -   tearing off by a gas flow that shears a liquid surface that        contains solid elements;    -   evaporation, during which diffusion of liquid molecules to the        gas environment entrains particles (dry extracts) to the gas        environment, as long as the partial pressure has not reached its        saturation level.

Therefore the operating conditions of a CIJ printer, particularly of themulti-jet type, impose severe constraints on management of solventconsumption related to fast evaporation resulting from the jet curtain.

It can be considered that the saturation level is reached in severalphases: firstly, splashing at the interface (gas/liquid/solid substance)generates droplets (of inks) that then evaporate tending to fill in thepartial pressure. This process can generate a very wide range ofdiameters of more or less wet particles. The next step is very smalldiameter particle coalescence processes (due to Brownian movements);these processes associated with the condensation by nucleation mechanismmake very small particles disappear; sedimentation is associated withevaporation (see Table 1) to make large particles disappear. Inparticular, this table shows that the settling speed depends on thesquare of the particle diameter.

TABLE 1 d (μm) v (m/s) 0.1 8.80E−07 0.5 1.00E−05 1 3.50E−05 5 7.80E−0410 3.10E−03 (source R C Flagan: Fundamentals of air pollutionengineering, page 300)

Consequently, the diameter of particles to be treated varies between 10nm or a few tens of nm and a few hundred nm (or 1 μm), that are notvisible to the naked eye. The distribution of particle sizes wasconfirmed by tests, and is typically centred on 400 nm.

P. C. Reynor and D. Leith, in “The influence of accumulated liquid onfibrous filter performance”, Journal of Aerosol Science, vol. 31, No.11, pp. 19-34, 2000, modelled the wet aerosols filtration process in afilter as illustrated in FIG. 3.

This diagram represents the filtration process in general, unrelated toany application to CIJ printers. In FIG. 3, the filter inlet flowcontains air, solvent vapour, aerosols (wet particles and droplets, withor without dry extracts).

In this scheme, large droplets (or aerosols), are intercepted and thedry part contributes to the formation of the “cake”, locally or on alarge area of the filter. The consequence of such saturation is areduction in the number and/or diameter of pores that enable passage ofthe flow and therefore a reduction in the effective surface area of thefilter, which increases the flow rate, increases the head loss andaccentuates entrainment of particles to the downstream side of thefilter; thus the required filtration function stops working.

At the filter outlet, the medium is composed of vapour and drops, someof which are not collected, while others will make up the flow ofdrained liquid. And there is a risk of introducing particles in thevapours that originate from drops forming the drained liquid.

There is also a practical problem in evacuating drained liquid to theink reservoir because the reservoir is at higher pressure than thefilter outlet zone.

Secondary aerosols can be created by evaporation of the condensatecontained in the membrane. This forms the mechanism for transfer ofaerosols to the downstream side. Consequently, the migrated drops willrelease charged particles by an evaporation effect and/or the filtermedium will be saturated with humidity and trapped particles, making thehead loss unacceptable for the application.

Pure gas and dry steam can pass through the membrane, withoutintroducing any pollution downstream from the filter (see the arrow atthe top of FIG. 3).

The particles and/or aerosols that will be deposited on the fibres ofthe filter membrane (by the interception mechanism) can be dissolved bythe solvent originating from condensation, and can be entrained by thissolvent that migrates to the outlet under the effect of pressure.Evaporation of the pure solvent part only generates pure vapour. On theother hand, the condensate containing particles evaporates once it islocated at the filter outlet, so that particles can be released and thuspart of the filtration function is lost (in FIG. 3, an intermediate“Evaporation” part joins the vapour part indicated by the top arrow,while another intermediate part (“Uncollected drops, Re-entrainment”)joins the aerosols and drops release arrow)

Condensed liquid that has not evaporated, is symbolised by the bottomarrow in FIG. 3: “Drained liquid”.

One solution consists of varying the flow configuration by increasingthe filter surface area with a folded structure (the filter then formsan accordion that increases the surface area of the membrane withoutcorrespondingly increasing the size), that reduces the flow velocity.This firstly increases the capacity to contain filtered particles, andsecondly slows the increase in the head loss so as to increase the lifeof the component to an acceptable level.

However, the inventors have observed that drainage to the downstreamdirection (as is FIG. 3) is not compatible with the anti-pollutionfunction. As explained above, it is possible that particles are releasedin the gas flow; furthermore, the pressure on the downstream side ishigher than the pressure on the upstream side, therefore it is difficultto pump on the downstream side. It can also be noted that the operatingconfiguration in a CIJ printer is not operation in a dry state for whichthe filter material supplier can guarantee a high efficiency of morethan 99.97%; and this efficiency is accentuated as a cake of filteredparticles is formed progressively.

Furthermore, observations made could not justify a compromise betweenthe dimensions of the filter system and its life (decided upon based onthe head loss and/or the time before occurrence of pollution released tothe downstream side).

The invention discloses a device for recovery of the atmospherecontaining solvent vapours from a printer or at least one print head ofa printer or at least one ink recovery reservoir from at least one printhead of a printer, comprising:

-   -   n (n≥1) filter(s), that will be arranged at the outlet from at        least one ink reservoir, each filter comprising an inlet face,        an outlet face and a filter body between these two faces, the        atmosphere to be filtered passing through the inlet face, and        then the filter body and the outlet face.

The invention applies, here and in the remainder of this application toa print machine, in particular to ink jet printers, one example being aCIJ printer.

For example: n=2.

Each filter, or the device for recovery, may comprise means ofrecovering at least part of the liquid condensed on its inlet face,and/or to eliminate at least some of this liquid, before it passedthrough the filter.

A filter in a device according to an aspect of the invention is mainlyfor separating solid particles from gas.

A wet flow in the filter, by direct interception or by condensation,would entrain particles in the depth of the filter, and one aspect ofthe invention assures that intercepted particles do not pass through thefilter material and exit from the downstream side (or on the side of theinlet face). In other words, a means is provide to eliminate not onlythe condensed humidity through the inlet face, but also the particlescontained in it.

Therefore the invention can be used to make a closed loop so as torecycle air drawn in through the gutter of a printer, for example a CIJtype printer, particularly a multi-jet printer, this recycling cleaningair that is sent (back) to the print head(s).

The filter, or each of said filters, can be placed on the upstream ordownstream side (considering the direction of circulation of theatmosphere or air in the recovery circuit) of solvent extraction means.These means can extract solvent from an inlet gas flow and producefirstly liquid solvent and secondly a gas flow in which the content ofsolvent vapour is lower than that in the inlet flow. These means are forexample condensation means or adsorption means or membrane separationmeans.

In the first case (filter located upstream from the solvent extractionmeans), the atmosphere to be filtered exits from the reservoir and thefiltered gas is sent to the solvent extraction means.

In the 2^(nd) case (filter located downstream from the solventextraction means), the atmosphere to be filtered exits from the solventextraction means and the filtered gas is sent to at least one printhead.

Such a device in which n>1, may also comprise means of selecting asingle filter to treat the atmosphere or gas to be filtered, that canfor example exit from the reservoir or one of a number of reservoirs orfrom the solvent extraction means (according to one of the 2 casesenvisaged above).

According to one embodiment, said recovery means may bring at least partof the liquid condensed on the inlet face of each of the n filter(s) toa reservoir.

Means can also be provided to direct the liquid that flows by gravityfrom the filter inlet face, to this reservoir.

This recovery reservoir can be the reservoir from which the atmosphereor gas to be treated originates; it is preferably a 2^(nd) reservoirdifferent from the 1^(st) reservoir (from which the atmosphere or gas tobe treated originates), to better manage viscosity (otherwise, solventis added into the 1^(st) reservoir without any control over what isadded). Thus, means can be provided, for example one or more conduitscalled separation conduits, to send a vapour or gas to be treated to thefilter(s), while a liquid, for example resulting from cleaning a filter,is sent to the 2^(nd) reservoir but not to the 1^(St) reservoir.

The filter is not saturated with particles initially, but duringoperation, humidity and particles captured by the filter reduce thefilter passage area, increasing the flow velocity and tending to degradethe equilibrium created in the first place when the filter was in thenew (or fresh) condition. Consequently, means may be provided for online cleaning of the filter(s).

A device according to the one particular embodiment of the invention canalso comprise the following, for the above purpose:

-   -   means of bringing or introducing some of the liquid outlet from        solvent extraction means or from a solvent reservoir, through        the outlet face of at least one filter, or of each filter and        then through said filter(s);    -   and/or means of bringing or introducing some of the gas outlet        from solvent extraction means or from a gas reservoir, or gas        filtered by another filter, through the outlet face of at least        one filter, or of each filter of a plurality of filters, and        then through said filter(s).

Thus, products are used which originate from solvent extraction means,for example products that result from condensation in these solventextraction means (for example in the case of filters located upstreamfrom the solvent extraction means), or solvent from a solvent reservoir(for example in the case of filter(s) located downstream from thesolvent extraction means), to clean one of the filters from its outletface.

Drying is done using some of the gas outlet from the solvent extractionmeans (for example in the case of several filters upstream from thesolvent extraction means), or from a gas reservoir (for example in thecase of a single filter located upstream or downstream from the solventextraction means), or that is sent to the print head after having beenfiltered by another filter (for example in the case of several filterslocated downstream from the solvent extraction means).

Regardless of the configuration, a reverse current of solvent can thusbe introduced (in the direction opposite the normal direction of gascirculation in the filter when this gas is being filtered) to flush outparticles trapped in the mass of the filter, towards its inlet face.

A reverse current of gas can also be introduced (also in the directionspecified above) to dry the filter and thus restore it to a cleancondition similar to its new condition.

This active maintenance action eliminates the portion of uncollected orre-entrained droplets. Otherwise, particles will be brought to theoutlet face of the filter.

For the case in which n>1, a device according to the invention maycomprise means of selecting a channel in which:

-   -   some of the liquid output from the solvent extraction means or a        solvent reservoir will be circulated to the output face of only        one of the filters;    -   and/or some of the gas output from the solvent extraction means        or from a gas reservoir, or that is sent to the print head after        having been filtered by another filter, will be circulated to        the output face of only one of the filters.

Preferably, when n>1, the different filters communicate with the sameatmosphere (through their input side).

Means can also be provided:

-   -   for selecting a 1^(st) filter to treat an atmosphere to be        filtered, for example output from the reservoir or from solvent        extraction means,    -   while the means of selecting a circulation channel to the outlet        face of another of the filters, are used to select a circulation        channel, towards the outlet face of another filter, different        from the 1^(st) filter, of part of the liquid output from the        solvent extraction means (for cleaning) or part of the gas (for        rinsing).

For the case in which n>1, a device according to the invention maycomprise means of selecting filtering of the atmosphere to be filteredby one 1^(st) filter, and means of simultaneously cleaning anotherfilter, different from the 1^(st) filter.

In a device according to the invention, the means of recovering at leastpart of the liquid condensed on the inlet face of at least one, or ofeach, filter may comprise means of recovering a liquid flowing bygravity from the inlet face of the filter.

The invention also relates to a circuit to supply at least one printhead (of a print machine, in particular an ink jet printer, for examplea CIJ printer), comprising:

-   -   at least one reservoir, to recover ink not used for printing and        to supply at least one print head;    -   a recovery device of the atmosphere originating from at least        one reservoir, according to one of the embodiments presented in        this application.

The invention also relates to a printer, in particular to an ink jetprinters, for example of the CIJ type, comprising at least one printhead, for example an ink-jet print head, in particular of a CIJ printer,and a circuit according to the invention, the head comprising means forforming k jets, where k≥1.

The invention also relates to a method for recovery of the atmospherecontaining solvent vapours from a printer, or from at least one printhead of a printer or from at least one ink recovery reservoir from atleast one print head of a printer, comprising:

-   -   filtration of an atmosphere output from at least one ink        reservoir of the printer making use of at least one filter, this        filter comprising in inlet face, an outlet face and a filter        body between these two faces, the atmosphere to be filtered        passing through the inlet face, and then the filter body and the        outlet face.

The printer can be in particular an ink jet printer, one example being aCIJ printer.

Preferably, at least part of a liquid condensed on the surface of theinlet face of the filter is recovered, before this liquid has passedthrough it.

The flow velocity being inversely proportional to the area of thefilter, the filter can be sized to be large enough to limit thevelocity. The entrainment of the condensate into the depth of the filteris thus minimised: this entrainment makes particles migrate to theoutput side of the filter and is an unwanted phenomenon. Imposing asurface area of the filter above a specific value therefore helps toachieve the required equilibrium state. Indeed, one problem is themigration of particles from the input side to the output side of thefilter, which is amplified by the gas flow velocity through the filter.For a given flow rate, a surface area is therefore preferably selectedso as to have a low flow velocity, for example <0.1 m/s.

In a printing process according to the invention, printing with aprinter is performed while a method according the invention is performedfor recovering of the atmosphere containing solvent vapours from theprinter. The filter(s), or each of said filters, can be placed on theupstream or downstream side (considering the direction of circulation ofthe atmosphere or air in the recovery circuit) of the solvent extractionmeans. As explained above with reference to the device, these means canextract solvent from an inlet gas flow and produce firstly solvent thatcan be liquid and secondly a gas flow in which the content of solventvapour is lower than that in the inlet flow. These means are for examplecondensation means or adsorption means or membrane separation means.

In the first case (filter located upstream), the atmosphere to befiltered is output from the reservoir and the filtered gas is sent tothe solvent extraction means.

In the 2^(nd) case (filter located downstream), the atmosphere to befiltered is output from the solvent extraction means and the filteredgas is sent to the print head.

The following can be introduced into the filter or into at least one ofsaid filters through its outlet face:

-   -   part of the liquid that exits from the solvent extraction means,        respectively from a solvent reservoir, to clean the filter;    -   and then possibly part of the gas that exits from the solvent        extraction means or from a gas reservoir, respectively of gas        filtered by another filter, to dry the filter.

Thus, the products (particularly the solvent) used are derived fromsolvent extraction means, for example by the condensation effect (forexample in the case of filters located upstream from the solventextraction means), or solvent from a solvent reservoir (for example inthe case of filter(s) located downstream from the solvent extractionmeans), to clean one of the filters from its outlet face.

Rinsing can be done using part of the gas output from solvent extractionmeans (for example in the case of several filters upstream from thesolvent extraction means), or from a gas reservoir (for example in thecase of a single filter located upstream or downstream from the solventextraction means), or that is sent to the print head after having beenfiltered by another filter (for example in the case of several filterslocated downstream from the solvent extraction means).

Therefore the filter can be regenerated by performing a maintenanceoperation, namely rinsing with solvent and drying.

When n>1, a channel for circulation of part of the cleaning liquidand/or part of the rinsing gas to only one of the filters can beselected.

For example, a 1^(st) filter is selected to treat the atmosphereoriginating from or output from the reservoir, and a channel is selectedto circulate, to a 2^(nd) filter (different from the 1^(st) filter),part of the liquid output from solvent extraction means or from asolvent reservoir respectively, or part of the gas output from solventextraction means or that is sent to the print head after having beenfiltered by the 1^(st) filter. When n>1, the atmosphere output from thereservoir can be filtered by a 1^(st) filter, and a 2^(nd) filter(different from the 1^(st) filter) can be cleaned at the same time.

Printing can therefore be performed while at least one of the filters isbeing cleaned, at least one other filter filtering the atmosphere outputfrom the reservoir.

According to one particular embodiment, at least part of the liquidcondensed on the inlet face of each filter flows by gravity from theinlet face of the filter and is possibly directed to the reservoir. Thisis advantageously achieved by inclining the filter such that its inletface is facing the reservoir from which the air to be treated comes.

The liquid that flows by gravity from the inlet face of the filter tothe reservoir can be recovered firstly by a liquid-gas separator placedbetween the filter and the reservoir.

The condensate created by the filter device (the membrane and thestructure) can be the main contributor to drainage, thereby allowingevacuation of some of the trapped particles. The dynamic equilibrium ismade as a function of the “chosen” side on which the drainage isevacuated, using the following elements:

-   -   the surface area of the filter imposes the initial flow        velocity,    -   the inclined position of the filter reinforces the effect of        gravity, forces moisture to be evacuated to the upstream side,        and slows the migration of particles to the downstream side.

The solvent recovery reservoir from the inlet face of the filter(s) canbe the reservoir from which the atmosphere or the gas to be treatedoriginates; it is preferably a 2^(nd) reservoir, different from the1^(st) reservoir (from which the atmosphere or gas to be treatedoriginates), so as to not disturb the viscosity in this 1^(st)reservoir. Thus, a vapour or a gas to be treated by the filter(s) can beseparated from a liquid (or solvent) resulting for example from cleaninga filter, to send this liquid to the 2^(nd) reservoir.

The embodiment in which a filter is positioned upstream of the solventextraction means is advantageous; in particular, it enables the filterto be rinsed by solvent droplets originating from the gas flow. It meansthat the gas flow saturated with solvent (but without condensationbefore entering the filter module) can be treated, which will createhumidity by natural condensation (in particular if the ink reservoir isthe hottest point in this part of the circuit); this humidity is usefulto create a liquid current on the inlet surface of the filter,continuously entraining surface particles to the drainage channel. Onthe other hand, more humidity would accentuate the phenomenon of closingpores in the filter, increasing the flow velocity, and would limit ordestroy the natural drainage mechanism. In other words gas containing,or being loaded with, solvent condensation at the input side of thefiler (which is at lower temperature than the ink reservoir) isfavourable to entrain surface particles; but too much condensation wouldsaturate the filter and close the pores of the filter.

In a printing process according to the invention, printing is stopped toclean the filter (if there is only one filter) and then printing isresumed after cleaning. If there are at least 2 filters, printing can becontinued while at least one filters is being cleaned, at least oneother filter filtering the atmosphere output from the reservoir or fromthe separator.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the invention will become clear from the descriptionof details of an example embodiment of the invention given below withreference to the appended drawings among which:

FIG. 1 is a perspective view of an inkjet printer known in prior art,

FIG. 2 represents a diagrammatic isometric view of a print head, showingprincipally the components of the print head located downstream from thenozzles,

FIG. 3 represents a filter and fluid flows upstream and downstream fromthe filter,

FIG. 4A represents a filter and evacuation, at, or from, the front faceof the filter, of the humidity deposited on said front face, before itpasses through the filter; FIG. 4B represents a housing for a filteraccording to the invention,

FIG. 5A represents the structure of a solvent recovery circuit accordingto the invention, with a filter placed on the upstream side of thesolvent extraction means,

FIG. 5B represents a variant of a structure of a solvent recoverycircuit according to the invention, with a filter placed on the upstreamside of the solvent extraction means,

FIG. 5C represents a variant of a structure of a solvent recoverycircuit according to the invention, with 2 filters placed on theupstream side of the solvent extraction means,

FIGS. 6A and 6B represent embodiments of a solvent recovery systemaccording to the invention, with two filters (FIG. 6A) and with a singlefilter (FIG. 6B) upstream from the solvent extraction means,

FIG. 7 represents an embodiment of a system for recovery of solventaccording to the invention, with 2 filters on the downstream side of thesolvent extraction means,

FIG. 8 represents an example of an SEM image of the inlet face of afilter after 48 h of operation, in the case in which the filter isplaced on the downstream side of the solvent extraction means,

FIG. 9 represents the variation of the head loss in the case in whichthe filter is placed on the downstream side of the solvent extractionmeans,

FIGS. 10A-10B represent examples of SEM images of the inlet face of afilter after 20 h of operation, in the case in which the filter isplaced on the upstream side of the solvent extraction means,

FIG. 11 represents of the variation of the head loss in the case inwhich the filter is placed on the upstream side of the solventextraction means,

FIG. 12 represents a head loss oscillation phenomenon, corresponding tothe moisture contents of a filter,

FIG. 13 represents the variation of the head loss after having startedwith a filter that has been rinsed but not dried,

FIGS. 14A-14D represent examples of SEM images of inlet and outlet facesof a filter, after 20 h of operation and with two different inks,

FIG. 15 represents the effect of a rinsing procedure on filters placedupstream from the solvent extraction means, on the transmembrane headloss

FIGS. 16A and 16B represent examples of condenser structures that can beused in the framework of this invention,

FIG. 17 represents an example structure of a fluid circuit to which theinvention might be applied.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

A first aspect of the invention will be explained with reference to FIG.4A, on which reference 20 designates a filter through which a flowpasses composed of vapour and droplets.

This filter comprises an inlet face 21 and an outlet face 22. The floworiginates from a ink reservoir 10 of an inkjet printer. This flow canbe high because, as mentioned above, it can be as much as several tensof liters per hour or several hundred liters per hour for a binarycontinuous jet printer.

At the outlet from this filter, the medium is composed of vapours anddroplets (of vapour condensate). There may also be entrained dropletscontaining particles; these particles may be among particles collectedby filter fibres separated by the presence of humidity from the solvent;evaporation of this humidity can return aerosols in the gas flowdownstream from the filter.

The liquid that is deposited or that condenses at the inlet surface 21of the filter can be eliminated from this inlet surface before it haspassed through the filter 20. It is evacuated through one or severalconduit(s) 25, for example to return to the ink reservoir 10, or to bedirected to a device such as an evaporator (then to the ink reservoir10), as explained below. This is the case particularly when theentrainment force towards the internal part of the filter (that isdependent on the flow velocity) is smaller than the force due togravity,

Preferably, a non-woven multi-layer fabric made of glass fibres (ornano-fibres) is chosen. Such a filter is chemically compatible withsolvents currently used in inkjet printers. A Teflon or polypropylenefilter could also be used. As a variant, it would also be possible touse a filter made of a woven material, but the average fibre diameterwould be larger.

For example, the thickness of the filter 20 can be between 100 μm and 1mm, and for example approximately 400 μm.

Also preferably, the air filter is compatible with the solvent.

“EPA” (Efficiency Particulate Air) filters, “HEPA” (High EfficiencyParticulate Air) filters and “ULPA” (Ultra Low Penetration Air) filterssatisfying standard NF EN1822, can be used. For example, reference canbe made to:www.boutique.afnor.org/norme/nf-en-1822-5/filtres-a-air-a-haute-efficacite-epa-hepa-et-ulpa-partie-5-mesure-de-l-efficacite-de-l-element-filtrant/article/619183/fa157748.

Fibre diameters are preferably between a few nanometers and a fewmicrometers, for example between 5 nm and 5 μm or 10 μm, to satisfy theneed for efficient blocking of particles while maintaining an acceptablehead loss. The distribution of pore sizes depends on the method ofmanufacturing the filter material. SEM observations show that the poresize in a layer is of the order of 1 μm. It is difficult to estimate thereal size of pores, considering that the filter material is made bysuperposing several layers. The filter material can create paths thatforce particles to follow very sinuous trajectories, which stimulatesthe interception mechanism. An unwoven structure has a very wide varietyof porosities depending on the distribution of fibre diameters, thusporosities of between less than 1 μm and a few tens of μm are observed(for example 10 μm). It is interesting to use this type of material(unwoven) because, starting from a given thickness equal for example toabout 400 μm, random porosities will create a resemblance between thedifferent sinuous passageways and, through the mechanism that wedescribed above (interception/impact, etc.), will stop almost allparticles within the range of diameters of interest (about 300 nm), andwill block larger particles (by the sieve and filter effect).

Refer to the course given in:cerig.pagora.grenoble-inp.fr/tutoriel/non-tisse/page01.htm.

As indicated in FIG. 4A, the filter 20 defines a plane that can beinclined from a horizontal direction by an angle α, for example between10° and 80°, for example between 40° and 60° (or between 30° and 80°).In general, recovery of humidity from the front face of the filter dueto the action of gravity, is facilitated if the inlet surface 21 of thefilter is inclined downwards during use of the filter, and the outletface 22 is facing upwards. This is why means are provided to keep thefilter inclined, such that humidity deposited on the front face can flowby gravity.

As a variant, the angle α can be zero (in which case the filter ispractically horizontal), which facilitates the recovery of liquid fromthe inlet face of the filter.

FIG. 4B shows a housing 250 in which the filter can be maintained. Thishousing comprises a 1^(st) face 251 called the inlet face, and a 2^(nd)face 253 called the outlet face. It comprises an inlet channel 252 onthe inlet face that also acts as an outlet channel for humidity that isdeposited on the inlet surface of the filter and that is evacuated. Itcomprises an outlet face 253, an outlet channel 254 and an inlet channel256 on the same side, for example close to the outlet channel 254, so asto introduce a cleaning and rinsing flow as explained below. Thishousing can contain a filter 20 represented in dashed lines in FIG. 4B.Means (support, arms; etc.) not shown keep the housing in the requiredposition.

The housing 250 plays a confinement role, and also provides leaktightness, directivity and thermal and mechanical stability.

FIG. 5A represents an environment in which a filter of the typedescribed above can be used.

This FIG. 5A shows the print head 1 and the catcher 7 that are showndiagrammatically.

Reference 10 designates an ink reservoir into which ink not consumedduring printing will be directed from the catcher 7.

This figure and subsequent figures show a single reservoir 10 and asingle print head 1, but a device or a method according to the inventioncan be equally applicable to the treatment of a flow from severalreservoirs 10 that recover ink and/or solvent from one or several printheads. For example, at least 2 reservoirs like reservoir 10 can besupplied in parallel at the outlet from the catcher 7, and this supplycan be provided by a pump. Similarly, the atmosphere or the gas treatedby a system or a method according to the invention can be sent to oneprint head (as described above), or to several print heads.

As explained above, the volume of the print head 1 communicates with theexterior through the orifice or the slit through which the jet(s) passto enable printing. An air exchange occurs with the atmosphere outsidethe head, though this slit or this jet outlet orifice; more precisely,gas containing solvent vapour escapes through this channel, whileexternal gas is mechanically sucked into the head through the samepathway to compensate for the lost flow; this suction will introducehumidity into the system.

A flow 11 of vapours from this reservoir 10 is directed to the filter20. In return, a liquid flow that is condensed on the inlet surface 21of the filter is carried to the reservoir 10 by ducts such as means 25,252 shown diagrammatically on FIG. 4B.

At the outlet from the filter, the flow of filtered vapours is directedto the solvent extraction means 26 (for example condensation means),that will condense solvent vapours and produce clean gas 35 that can bereturned to the print head 1. It is said that the filter is positionedupstream from the means 26, since the vapours 11 to be treated firstlypass through the filter, and the filtered flow 27 is then directed tothe means 26. The solvent extracted (for example by condensation) canthen be carried to the reservoir 10 through an evacuation line 29 thatcould be provided with a pump 28. In this case and in the otherembodiments presented in this application, the solvent extraction meansused may be any means of denaturing a solvent in a gas flow containingit, or any means of extracting a solvent from a gas flow or lowering theconcentration of solvent in such a flow, for example by membraneseparation or adsorption. The remainder of this description applies tocondensation means (or a condenser) but all these other examples ofsolvent extraction means can be used to produce solvent extracted fromthe gas flow and a gas flow with a reduced solvent concentration.

Part of the liquid solvent resulting from condensation in the condenser26 can be used to be transferred through a line 31 that can be fittedwith a pump 30, to the outlet face 22 of the filter in preparation for acleaning operation of this filter.

Clean gas 35, output from a gas storage or reservoir 37 can be sentthrough a line 33 and a pump 32, to the outlet face 22 of the filter 20,for a drying operation after a possible cleaning operation.

The pumps and the valves, if any, can be controlled by means forming theprinter controller and programmed for this purpose.

The parts of the pathways 31, 33 closest to the filter 20 can becoincident.

A filter cleaning method according to the invention can be used. Such amethod can regenerate a spent filter that can be clogged by solid and/orliquid aerosols, to prolong its life.

To achieve this, the supply to the filter by a flow 11 from thereservoir 10 is cut off. For example, the atmosphere on the side of theinlet face 21 of the filter is brought to atmospheric pressure so thatthe flow 11 no longer passes through it.

The filter is then rinsed by injection of solvent through its outletface 22. This solvent will pass through the filter 20 and act so as totake away polluting elements that could be trapped in its mass. Thedirty solvent flow output from the inlet face 21 can then be sent to theink reservoir—for example passing through a separator (as describedbelow) so that the evaporated solvent, and the dry material contained inthe solution, can be returned to its source. Preferably, this is doneusing some of the purified solvent that can be recovered from thecondenser 26 (through the line 31 and the pump 30 in FIG. 5A). Accordingto one embodiment, when the filter is inclined at an angle α (asillustrated for example in FIG. 4A), the solvent can be carried to thehighest end of the outlet face 22, from where it can run down over thisentire face 22.

The filter can then be dried, for example using the compressed airsource 37 and possibly a pump 32.

During these cleaning operations, the inclination of the filtersymbolised by the angle α that can be seen on FIG. 4A, can play a role:if the filter is almost vertical (for example angle α between 60° and90°), or if it is almost horizontal (for example angle α between 0° and30°), one of its ends might not be cleaned, particularly if a techniquesuch as runoff (or run down) described above is used for cleaning. Theangle α for these cleaning operations is preferably between 30° and 80°.A variable angle can be provided depending on the operations to be done,for example: 0° during filtering, then 60° during cleaning.

A variant of part of the device in FIG. 5A is shown in FIG. 5B. This isthe pathway that carries vapours from the reservoir 10 to the filter 20.In the structure in FIG. 5B, a separator 40 is placed between thereservoir 10 and the filter 20. For example, this separator functions byinertial precipitation. It can separate the largest particles containedin the atmosphere arriving from the reservoir 10. Thus, vapours fromwhich the largest particles or pollutants have been removed are sent tothe filter 20. The remainder of the system can be as described withreference to FIG. 5A.

A variant of part of the devices in FIGS. 5A and 5B is shown in FIG. 5C.In this case, two filters 20, 20 a are used in parallel. This type ofassembly can allow the use of one filter while a cleaning procedure isbeing applied to the other filter, as described above.

To achieve this, each filter (that can be contained in a individualhousing like that described above with reference to FIG. 4B, fitted withconnections to connect fluid supply and return conduits), can besupplied through a conduit 11, 11 a from the reservoir 10 or theseparator 40. Each filter is associated with an outlet conduit 27, 27 athat is connected to an inlet of a three-way valve 45, the output ofwhich carries the gas flow selected by the valve 45 away to thecondenser 26, through a conduit 27′.

Each filter may be associated with a 1st return pathway through whichthe cleaning fluid (purified solvent) can be sent to the outlet face 22,22 a of the corresponding filter and/or with a 2nd return pathwaythrough which clean rinsing gas can be sent to the same output face 22,22 a of the corresponding filter, so that the cleaning or rinsingoperations as described above can be performed, if necessary.

The filter towards which the rinsing/drying liquid/gas will be sent isselected by means 47 (for example a valve or a solenoid valve), theinputs of which are supplied through the pathways 31, 33 that are,connected to the condenser 26 and to the line through which the gasesoutput from the condenser 26 circulate after treatment in the condenser,respectively.

Such a system makes it possible to use filters 20, 20 a alternately, andalso clean them alternately. If a 1^(st) filter requires a cleaningoperation, the 2^(nd) filter is changed over (or switched) using means45, into a working situation (to filter vapours from the reservoir 10 orfrom the separator 40), and the 1^(st) filter can be cleanedsimultaneously as described above and then once again changed orswitched over to the filtering situation while a cleaning operation isperformed on the 2^(nd) filter. This alternation can be programmed by aclock with constant time intervals, and/or by means forming the printercontroller programmed specially for this purpose.

Both filters 20, 20 a are connected to the reservoir (not illustrated onFIG. 5C) and therefore communicate with the same atmosphere.

The set of the two filters in FIG. 5C can be combined with the meansalready described above with reference to FIGS. 5A and/or 5B.

FIG. 6A represents an embodiment of a system using 2 filters 20, 20 a,for example made of glass fibres, that are used in alternation.

On this figure, references identical to references in the previousfigures designate identical elements or elements performing the sametechnical function.

Both filters 20, 20 a are connected to the separator 40 and thereforecommunicate with the same atmosphere. On this figure, the reference 50designates a buffer volume in which condensation products from thecondenser 26 are recovered. This volume 50 can use a pump 30 to supplyfilters 20, 20 a ready to clean them, as described above. Reference 101designates a storage volume for an additive (for example solvent) incase a loss has to be compensated using an additive; a pump 67 pumpsadditive from this storage volume to add to the ink in the reservoir 10.

The reservoir 10 can be supplied with recovered ink pumped using a pump53 (for example a diaphragm pump) from the gutter in the print head 1.The flow in the recovery line is two-phase, with a flow equal to forexample between 0.3 and 10 liters/hour of liquid, and between 10 and10000 liters/hour of gas, for example 1000 l/hour. This two-phase flowis generated by the pump 53. The flow in this pathway and the inkreception mechanism (reception of the two-phase flow from a pipe in theink reservoir 10 create more or less from splashing—that in particularcan release large particles) can generate various sizes of aerosols, asdescribed above.

The reservoir 10 can supply the head 1 with ink through the pump 57 anda first filter 59 then a second filter 63, close to the print head. Asensor 61 measures the pressure in the supply pathway to the head 1.

The gas flow is then carried due to the positive pressure in thereservoir 10, to the filter 20 or 20 a connected with the open pathwayof the 3-way valve 45. This valve may for example be controlled using apredefined clock.

The gas flow is filtered in the selected filter 20 or 20 a and is thendirected to the condenser 26 through the open pathway of the valve 45. Amechanism for separation of condensates from desaturated air carries thecondensates in the buffer volume 50, and air through the return line 69,to the print head 1.

Another pathway starting from the buffer volume 50 directs a calibratedquantity of condensates through a pump 30 and controlled valves 47, tothe filter 20, 20 a waiting for maintenance (this is the filter forwhich the pathway from the 3-way valve 45 is closed). Therefore thesolvent flow follows a path opposite the path followed by vapours outputfrom the reservoir 10 or the separator 40 and that have to be treated byone of the filters 20, 20 a. Therefore this solvent flow passes firstlythrough the downstream side 22, 22 a of the membrane and then the filterbody, and is then directed to the upstream side 21, 21 a, cleaningparticles deposited on the surface 22, 22 a and in the depth of thefilter membrane. The dirty (but very dilute) solvent then passes throughthe separator 40 in counter current to the gas flow (that rises to thefilter in service). This solvent flow is thus useful to clean theseparator 40 to remove deposits of dry extracts deposited in it duringthe filter process.

It may be useful (in this case and in other embodiments of theinvention) to provide separation between rising vapour (from thereservoir 10) and the drainage (descending) from the separator 40 to asecond reservoir 10 a; a junction “settles” or decants the liquid so asto avoid directing it to the reservoir 10 (to avoid disturbing theviscosity in this reservoir 10). According to the embodimentillustrated, a 1^(st) conduit 11 a is followed by the liquid flowingfrom the separator 40 to the second reservoir 10 a; a 2^(nd) conduit 11b channels the gases to be treated from the reservoir 10 and joins the1^(st) conduit 11 a such that the gases continue to be channeled to theseparator 40 but the liquid from the separator cannot pass along the2^(nd) conduit 11 b. For example, the assembly is in the form of a ‘Y”,the bottom of the ‘Y” being oriented towards the second reservoir 10 aand one of the 2 branches being connected to the separator and the otherto the 1^(st) reservoir.

After the liquid has passed through the filter during rinsing, anotherpump 32 connects the desaturated gas pathway to the filters; this gas isdirected by two valves 47, for example controlled according to thepreconfigured clock. This drying mechanism can also open pores of thefilter membrane after having rinsed it.

The desaturated gas thus drawn off is returned to the separator, then tothe filter that is not in the maintenance phase.

Consequently, the air flow used starting from line 69 to dry one of thefilters in maintenance, circulates in a local loop, which will not haveany impact on the net flow transferred to the head 1. Air drawn off bythe pump 32 will generate a surplus flow through the filter inmaintenance, and is then transferred to the condenser 26 and returned tothe line 69, which compensates for the deficit generated by the pump 32.Air drawn off by the pump 32 also generates an overpressure in thereservoir 10 and/or in the separator 40, but also in the other filter,through which a higher flow rate circulates since both filterscommunicate with the same atmosphere (through the separator 40 in thisexample). As a variant, air can be brought in from the exterior and thentransferred by pumping to the required filter in preparation for drying.

The intensity of this gas flow in the local loop is preferablycontrolled to minimise the pressure fluctuation in the reservoir 10 andin the gas flow to the return from the print head 1.

The maintenance action is thus completed. The function of the cleanedfilter is regenerated, and this filter is ready to filter gas from thereservoir 10.

The 3-way valve 45 controls the changeover of the gas flow to the filterto be cleaned, and the maintenance function described above on the usedfilter can begin, to take advantage of the low head loss when the filteris fresh.

With this 2-filter system, the printer can continue to function (theprinting operations continue to be performed) without being hindered bycleaning operation on one filter: air continues to be filtered by theother filter and the head 1 can be supplied by air drawn from the outputfrom condenser 26 as explained above; therefore filtering can becontinuous, with one filter filtering while the other is being cleaned,and vice versa.

A cleaning method can be applied in the case of a system provided with asingle filter 20, as illustrated in FIGS. 5A and 5B. In this case, afilter sequence using the filter 20 is followed by a cleaning sequencethat is followed by another filter sequence, etc. The recovery circuitof vapours that exit from the filter can be provided with the condenser26, but also with the buffer reservoir 50, and means 30, 31, forreturning solvents recovered in this buffer volume 50 to the filter 20or the reservoir 10 (a further pump and a duct can be implemented totransfer solvents from reservoir 50 to reservoir 10) respectively.Similarly, the conduit 69 that supplies the head 1 is located at theexit from the condenser 26; the compressed gas reservoir 37 and the pump32 if there is one, dry the single filter 20 during a rinsing operationsubsequent to cleaning.

A system with a single filter can include means 53, 57, 59, 61, 63, 101,10 a, 11 a, 11 b described above with reference to FIG. 6A. FIG. 6Brepresents a variant embodiment of FIG. 6A, with a single filter.Therefore the system is simpler. The elements in FIG. 6B have alreadybeen described above, with FIG. 6A or with FIG. 5B (and particularly theexternal gas source 37). However, filtering cannot be continuous in thiscase, since operation of the filter is interrupted for cleaning usingsolvent recovered from the condenser.

A depressurisation path 103 is provided on the side of the ink reservoir10 to balance the pressure between the different parts, during thefilter maintenance phase. The valve 103 a is then opened and thereservoir 10 is at atmospheric pressure. The printing machine can thencontinue to print.

The solvent from the reservoir 50 can be sent to the reservoir 10through the separator 40 (valve 30 a opened, valve 30 b closed) or tothe filter 20 to clean the filter (valve 30 b opened, valve 30 aclosed).

The flux drawn off in the compressed gas reservoir 37 can be adjustedusing a valve 39 a, and preferably a proportional valve 39, 39 a.Compressed gas from this reservoir 37 can be used to supply the head 1.

FIG. 7 represents an embodiment of a system using two filters 20, 20 a,for example made of glass fibres, that are used in alternation, but thatare located downstream from a condenser element.

On this figure, references identical to references in the previousfigures designate identical elements or elements performing the sametechnical function.

In this embodiment of the invention, air or the atmosphere returned fromthe reservoir 10 is firstly desaturated by the condenser 26 before beingfiltered by one or the other of the filters 20, 20 a.

The outlet from each filter is sent to the print head 1 through anoutput valve 45 b that is a 3-way valve in the example shown. This valvemay for example be controlled with a predefined clock.

In this type of system, condensation originating from the front face ofthe filter according to the diagram shown in FIG. 4A, is firstlyrecovered by the condenser 26 and then by the separator 40 before beingredirected to the reservoir 10.

The additive reservoir 101 is used to transfer clean solvent to one orthe other filter 20, 20 a during a cleaning operation using pump 67 a,as explained above; a set of valves 47 a-47 d directs the solvent to onefilter or the other filter.

The solvent flow then follows the path followed by vapours outlet fromthe condenser 26 and that are to be treated by one of the filters 20, 20a, in the reverse direction: therefore it passes firstly through thedownstream side of the membrane 22, 22 a, then the filter body, and isthen directed to the upstream side 21, 21 a, cleaning particlesdeposited on the surface 22, 22 a and in the depth of the filtermembrane. The dirty solvent is then sent to the condenser 26 afterpassing through the filter that has just been cleaned.

After the liquid has passed through the filter during rinsing, a pump 32sends the desaturated and then filtered gas once again to one filter orthe other filter; this gas is directed by valves 47 a-47 d, for examplecontrolled according to the preconfigured clock. As in the previousexamples, this drying mechanism can also open pores of the filtermembrane after having rinsed it.

The maintenance action is thus completed. The function of the cleanedfilter is regenerated, and this filter is ready to filter gas from thecondenser 26.

The 3-way valve 45 b sends the gas flow from the cleaned filter to thehead 1, and the maintenance function of the other used filter can begin.

As in the case in FIG. 6A, with this 2-filter system, the printer cancontinue to function without being hindered by cleaning operations onone filter: air continues to be filtered by the other filter and thehead 1 can be supplied by filtered air as explained above; thereforefiltering can be continuous, with one filter filtering while the otheris being cleaned, and vice versa.

But in this configuration with filters located at the outlet from thecondenser 26, cleaning of the filter must be more frequent than when thefilters are located at the inlet to the condenser 26, since the filtersdo not benefit from the action of a wet flow and thereforeself-cleaning.

A system can also be made (not shown) using a single filter 20; forexample made of glass fibres, located downstream from a condenserelement 26. As in the case in FIG. 6B, in this case filtering cannot becontinuous since operation of the filter is interrupted for cleaning bythe solvent from the solvent reservoir 101. A compressed gas reservoirlike the reservoir 37 in FIGS. 5A and 6B, supplies a drying gas flowafter cleaning by solvent. Once again, the filter is cleaned morefrequently than when the filter is located at the inlet to the condenser26, because it does not benefit from the action of a wet flow.

In general, when a device or a method according to the invention isused, it is preferred to keep the concentration of solvent vapour in thegas flow equal to a value lower than the saturation level at the lowesttemperature that can be found in the processing loop. A gas phase flowin this loop does not in any way compromise the treatment mechanismdisclosed according to the invention. To achieve this, it is preferredto simply prevent condensation in the part of the circuit downstreamfrom the extraction means 26 and as far as the head 1, rather than tocondense everything. The maximum concentration that should preferablynot be exceeded can be chosen to be equal to the saturatingconcentration at the temperature at the coldest point (always in thedownstream circuit). In other words, if the coldest point encountered bythe gas flow is located in the extraction means 26, there can be nocondensation downstream from these means 26. Adapted thermal means willmake it possible to satisfy this temperature condition.

Comparative tests will be presented, making used of the systemsdescribed below. These tests make it possible to understand theefficiency and the advantages of a filter system according to theinvention.

The ink used is either black ink with colorant, or white ink withpigments.

The reservoir 10 is fitted with a pressure sensor so that tests can becarried out on the structures described above. The pressure measurementthus obtained is a direct measurement of the head loss due to the filter20. When the filter becomes clogged, it will generate head losses thatwill pressurise the reservoir.

For example, the pressure sensor can be a GE UNIK 5000 type instrument(measurement range: 0-5 bars) with a sampling frequency of 0.5 Hz.

Furthermore, the filters were observed under a scanning electronmicroscope (SEM), that forms a qualitative means of evaluating theiroperation. The zoom level is adjusted to observe the fibrous structureof the filter, but also the particles that are deposited on it.

The different results obtained for the different usage conditionsdescribed above, are presented below.

In the case of a structure like that in FIG. 7 with the filterdownstream from the condenser 26, after 48 hours of operation with ablack ink with colorant without any maintenance, particles interceptedby the membrane form a “cake” on the side of the inlet face 21 of thefilter that increases the filtration capacity, but also increases thehead loss, until it becomes incompatible with the operation of an inkjetprinter. The output face 22 remains clean which confirms the efficiencyof the filter, even during the phase in which the head loss was low; inother words, by observing the cleanliness on the surface at the filteroutlet, it can be concluded that this material is efficient before thecake is formed.

An SEM photo of the inlet face of this membrane (FIG. 8, magnification45) also after 48 hours of operation without maintenance with a blackink with colorant, confirms that the filter is almost clogged byparticles with diameters varying from a few tens of nm to a few hundrednm. Cleaning according to the invention that is more frequent than in astructure in which the filter is placed upstream from the condenser 26can then by done.

It will be noted that the increase in the head loss through this filtershown diagrammatically in FIG. 9, reaches a level of 250 mbars in 24hours. Theory predicts that this trend continues with the formation ofthe cake of filtered particles. The filter thus becomes hermeticallysealed for the gas flow. This test was not done with a pressure sensorat all times, which explains why there are not many points on FIG. 13.

Therefore a filter positioned on the return path to the head after thecondenser clogs more quickly; consequently, cleaning is done earlierthan in a structure with a filter placed before the condenser.

In the case of the structure in FIG. 5A (filter upstream from thecondenser), after 20 hours of operation with black ink with colorant, itis seen that the open part of the membrane (FIG. 10A: SEM photo withmagnification of 45) remains practically identical to the open part of anew filter. Pollution zones are local, or in the form of clumps orclusters (FIG. 10B: SEM photo with magnification of 3500).

FIG. 11 shows the variation of the head loss due to the filter when itis located upstream from the condenser 26 and no maintenance is done onit, as a function of the operating time starting from a new filter. Thisfigure clearly shows that the head loss increases relatively slowly.After about 24 h, the pressure in the reservoir is more than 80% lowerthan the pressure obtained when the filter is operating in dry mode, inother words when it is located downstream from the condenser as in FIG.7 (compare the results in FIG. 11 with the results in FIG. 9).

It can be noted that the condensation process can already stop some ofthe particles; therefore it is preferably to make the filter operate inthe wet state, in other words to use a filter placed upstream from thecondenser 26; but as explained elsewhere, the filter can also beoperated in a dry state, in other words a filter can be placeddownstream from the condenser 26.

Globally, the head loss with the filter positioned upstream from thecondenser, is not excessive. In the configuration using white ink withpigments (FIG. 12), but without separator 40, an oscillation phenomenonwas also observed starting after about 5 hours of operation. This canprovide first information about a limiting operating time of the filter(positioned upstream from the condenser) that can therefore, forexample, be between 1 h and 10 h, or between 3 h and 7 h.

The increase in the head loss depends on the degree to which pores areclosed off by the liquid, oscillation results from the accumulationphenomenon followed by evacuation downstream from the filter under theeffect of pressure.

This oscillating phenomenon can be explained by an unstable state ofoperation of the membrane filter; the increase in the trans-membranepressure is followed by a release, as if drainage took place through theoutlet face 22.

Various tests and observations confirm the above analyses. A directsupply of a wet flow to the membrane (droplets output from the reservoir10, condensation created in the filter housing) saturates the membranewith solvent. If the opening of some of the pores of the filter stilloccasionally allows the gas flow to pass through (with a high headloss), depending on the rate of the supply of moisture, an “avalanche”effect can occur (in other words the reduction in pores correspondinglyaccentuates this reduction process by the increase in velocity, andmakes drops migrate to the remaining pores that are still open). In theshort term, it will cause complete closure of the passage area that willthen be subsequently unclogged by the increase in the upstream pressure.FIG. 12 illustrates stabilisation of the head loss accompanied by arelease of particles after about ten hours in the case of theconfiguration with a filter upstream from the condenser.

The variation in the head loss of black ink with colorant when thesystem (filtration system with filter upstream from the condenser)starts with a dry or dirty used filter from the previous day (see FIG.13). In this case, stopping the system will lead to an increase in thehead loss during the night. When restarting, the head loss is very high(about 100 mbars); and then the head loss reduces as the membraneabsorbs humidity to return to the equilibrium state (about 20 mbars).Therefore it can be concluded that the pores are relatively open duringoperation, and that they close during the night due to drying.

2 inks were used for another test, with pigments and with colorants, tostudy maintenance parameters for regeneration of the filter, in the caseof a configuration with 2 filters located at the outlet from theseparator (but without condenser) and the rinsing method according tothe invention described above.

SEM photos in FIGS. 14A-14D (magnification ×100) show “rinsed” filtersafter having operated for more than 20 hours. The front face 21 in blackink (FIG. 14A) and white ink (FIG. 14B) and the back face 22 in blackink (FIG. 14C) and white ink (FIG. 14D) are observed.

FIG. 15 illustrates the effect of rinsing on 5 cycles (regeneration ofthe filter function). The variation of the head loss takes place fairlysimilarly, suggesting that most of the filter function was restoredafter the rinsing operation.

This FIG. 15 shows that a filter can be restored several times afteroperation for a few hours, by rinsing with solvent and then by dryingwith dry air. It is observed that it is thus possible to maintain a headloss equal for example to approximately 15 mbars.

The time between two maintenance operations will generate a more or lesssignificant head loss and may or may not initiate the releasephenomenon. The filter area facing the gas flow is a parameter thanneeds to be integrated to guarantee a sufficiently low passage velocity(doubling the area will reduce the velocity to half, and the head lossto a quarter which stimulates, or is conducive to, the drainagephenomenon on the inlet face illustrated on FIG. 4A). Finally, thenature of the gas flow and particularly its content of droplets will usethe filter differently; the quantity of droplets in the atmosphere thatenters the filter has an effect on drainage and on the repeated releaseof impurities. If there are too many droplets, the filter is wetted morequickly which stimulates, or is conducive to, the repeated releasephenomenon; the maintenance frequency then has to be increased.

The behaviour of a filter 20 facing a gas flow saturated with solventvapours and located upstream from a condenser 26, was studied above.FIG. 11 confirms the efficiency of drainage that is developed in thisconfiguration by stabilising the head loss to a level of about 50 mbarsafter 24 h. FIGS. 10A-10B validate understanding of the drainagephenomenon because it is observed that the area of the filter membraneis almost unmodified and is always very open.

The impact of excessively high humidity on the filter has also beenshown, see FIG. 12. It is found that installing a device 40 to separatedroplets derived from condensation at the reservoir outlet 10 reducesthe average level of head losses.

Concerning the condenser 26 that can be used in a system according tothe invention, the condenser can be made in the form of a cylindricaldrum 262 inside which a number of ducts 264 has been formed, asillustrated in FIG. 16A. The cylinder is machined laterally so as todefine two plane faces 267 parallel to the axis of the cylinder andparallel to each other. These two plane faces will be used for coolingthe module.

The drum can be inserted in an approximately parallelepiped shapedretaining structure 266, the top and bottom parts 268, 269 have beenhollowed such that each of the two side faces of the drum can be broughtinto contact with a Peltier type cooling module 272, 274, as illustratedin FIG. 16B.

The hot face of the Peltier elements can be cooled using watercirculation in an aluminium block 276, 278 in contact with the face tobe cooled. A thermostat-controlled bath holds the temperature of thewater flow to the required temperature. Several elementary condenserslike that in FIG. 16A can be stacked, as illustrated in FIG. 16B. Theassembly can be placed between an inlet block 282 and an outlet block284, that allow inlet and outlet of the gas through an inlet orifice 286and an outlet orifice (not shown on FIG. 16B) respectively.

Air saturated with solvent vapours will circulate in the cooled channels264 of the condenser, and therefore the solvent will be condensed.

Regardless of what embodiment is envisaged, the instructionsparticularly to activate the print head to produce ink jets and thegutter pumping means 53 and/or the means 73 for sending a gas into theprint head and/or the means 57 for sending ink into the print headand/or the means 30, 32 of cleaning the filter are produced and sent bythe control means (also called the “controller”). These are theinstructions that cause circulation of ink under pressure towards theprint head, then generate jets as a function of motifs to be printed ona support 800 (FIG. 1). These control means may for example be made inthe form of a processor, or a programmable electric or electroniccircuit, or a microprocessor programmed to implement a method accordingto the invention.

This controller also controls opening and closing of valves on the pathof the different fluids (ink, solvent, gas), and operation of the meansof circulating a fluid in the filter means according to the invention(for example valves 45 and 47 in FIG. 6A or 6B), or pumps 30, 32, 51.The control means can also memorise data, for example data formeasurement of ink levels in one or more reservoirs, and process thesedata.

FIG. 1 shows the main blocks of an inkjet printer (for example acontinuous inkjet printer or CIJ printer) that can implement one orseveral of the embodiments described above.

Such a printer comprises a print head 1 (that can also have thestructure illustrated on FIG. 2) and means 200, 300, 400 of supplyingprinting ink to the head. The print head is connected to a recoverycircuit like that described above.

A printer according to the invention may comprise a console 300, acompartment containing particularly the ink and solvent conditioningcircuit 400, and reservoirs for ink and solvents (in particular, thereservoir to which ink recovered by the gutter is delivered). Ingeneral, this compartment is in the lower part of the console. The toppart of the console comprises the control and instrumentationelectronics and display means. The console is hydraulically andelectrically connected to a print head 1 through an umbilical 200.

Means for maintaining the head, for example a portal frame not shown,are used to install the print head facing a print support 800, whichmoves along a direction materialised by an arrow. This direction isperpendicular to an alignment axis of the nozzles. Preferably, thesemeans are controlled, through the controller, so that printing can beperformed on surfaces which are not flat, for example cables or bottlesor cans. In a preferred embodiment, these means can maintain thedistance (for example at least between 4 mm and 5 mm, in particular fora CIJ printer) between a printing head and the substrate which must beprinted higher than in conventional desk printers.

One example of a print head that can be used with a device or a methodaccording to the invention is illustrated in FIG. 2 and has beendescribed above.

An example of a fluid circuit 400 of a printer to which the inventioncan be applied is illustrated in FIG. 17. This fluid circuit 400comprises a plurality of means 10, 500, 110, 220, 310, each associatedwith a special function. There is also the head 1 and the umbilical 200.

This circuit 400 is associated with a removable ink cartridge 130 and asolvent cartridge 140 that is also removable.

Reference 10 designates the main reservoir, that collects a mix ofsolvent and ink.

Reference 110 designates means of drawing off and possibly storingsolvent from a solvent cartridge 140 and providing solvent thus drawnoff to other parts of the printer, either to supply solvent to the mainreservoir 10, or to clean or maintain one or several other parts of themachine.

Reference 310 designates all means of drawing off ink from an inkcartridge 130 and providing ink thus drawn off to supply the mainreservoir 10. As can be seen on this figure, according to the embodimentpresented herein, these same means 310 are used to send solvent to themain reservoir 10 and from the means 110.

At the outlet from the reservoir 10, a set of means globally designatedas reference 220 applies pressure to the ink drawn off from the mainreservoir and sends it to the print head 1 (these means compriseparticularly the pump 57, 59 in FIG. 6A or 6B above). According to oneembodiment illustrated herein by the arrow 250, it is also possible touse these means 220 to send ink to the means 310, and then again to thereservoir 10, which enables recirculation of ink inside the circuit.This circuit 220 is also used to drain the reservoir in the cartridge130 and to clean connections of the cartridge 130.

The system shown on this figure also includes means 500 of recoveringfluids (ink and/or solvent) that return from the print head, moreprecisely from the gutter 7 of the print head or the head rinsingcircuit. Therefore these means 500 are arranged downstream from theumbilical 200 (relative to the direction of circulation of fluids thatreturn from the print head). In particular, they include means 53 inFIG. 6A or 6B, but they can also include a solvent vapours treatmentcircuit according to one embodiment of the invention.

As can be seen in FIG. 17, the means 110 can also be used to sendsolvent to these means 500 directly without passing through theumbilical 200 or through the print head 1 or through the catcher.

The means 110 can comprise at least 3 parallel solvent supplies, one tothe head 1, the 2nd to the means 500 and the 3rd to the means 310.

Each of the means 500, 110, 210, 310 described above can be providedwith a pump to treat the fluid concerned (namely 1st pump, 2nd pump, 3rdpump, 4th pump respectively). These different pumps perform differentfunctions (the functions of each of their means) and are thereforedifferent from each other, even though these different pumps may be ofthe same type or similar types (in other words none of these pumpsperforms 2 of these functions).

Such a circuit 400 is controlled by the control means described abovethat are usually contained in the console 300 (FIG. 1).

The invention is particularly useful in applications in which the air orgas flow in the cavity in the print head and in the recirculationcircuit is high, since a high air flow creates a correspondingly largerrisk of allowing solvent to escape.

For example, the flow may be of the order of several tens of l/h orseveral hundred l/h, for example between 10 l/h and 10000 l/h, or forexample between about 300 l/h and 1000 l/h. These values areparticularly applicable to the case of a print head with 64 jets, butthe invention is also applicable to the case of a print head with asmaller number of jets, for example 16, or to the case of a print headwith a larger number of jets, for example 128.

The printers concerned by the invention are industrial printers, forexample which have the ability to print on surfaces which are not flat,for example cables or bottles or cans. Another aspect of such printersis that the distance between the printing head and the substrate whichmust be printed is higher than in conventional desk printers. Forexample that distance is at least between 4 mm and 5 mm for a CIJprinter.

Another aspect of such printers is their speed: their maximum speed isup to 10-15 m/s.

Another aspect of such printers is that they can print on very differentsurfaces, for example glass, or metal or blisters or packagingmaterials.

The invention claimed is:
 1. A device for recovery of an atmospherecontaining solvent vapours from at least one ink recovery reservoir of aprint machine comprising: n(n≥1) filter(s) arranged downstream from saidat least one ink recovery reservoir, each of said n filter(s) comprising: an inlet face, an outlet face and a filter body between said inletface and said outlet face, at least one duct to recover at least part ofa liquid condensed on the surface of said inlet face of one of said nfilter(s), before said liquid has passed through the surface of theinlet face of said one of the n filter(s), and each of said n filter(s)being: either upstream from solvent extraction means, an atmosphere fromsaid at least one ink recovery reservoir, passing through said inletface, and then through said filter body and through said outlet facebefore being sent to said solvent extraction means, or downstream fromsolvent extraction means, an atmosphere from said solvent extractionmeans passing through said inlet face, and then through said filter bodyand through said outlet face before being sent to at least one printhead of the print machine, respectively.
 2. The device according toclaim 1 in which n>1, and comprising at least a valve to select a singleone of said n filters to treat an atmosphere output from said at leastone ink recovery reservoir or from said solvent extraction means,respectively.
 3. The device according to claim 1, said at least one ductbringing at least part of the liquid condensed on said inlet face of atleast one of said n filter(s) to a reservoir.
 4. The device according toclaim 1, said at least one duct directing the liquid that flows bygravity from said inlet face of at least one of said n filter(s) to areservoir.
 5. The device according to claim 1, also comprising: acircuit to introduce some of the liquid outlet from said solventextraction means or from a solvent reservoir respectively, through saidoutlet face of at least one of said n filter(s); and/or a circuit tointroduce some of the gas outlet from said solvent extraction means orfrom a gas reservoir, or some of the gas filtered by another filter orfrom a gas reservoir respectively, through said outlet face of at leastone of said n filter(s).
 6. The device according to claim 5, in whichn>1, and comprising at least a valve to select a circulation pathway, tosaid outlet face of only one of said n filters: for some of the liquidoutlet from said solvent extraction means or from said solvent reservoirrespectively, or for some of the gas outlet from said solvent extractionmeans, or from a gas reservoir or from another filter respectively. 7.The device according to claim 6 comprising: at least a 1^(st) valve toselect a 1^(st) one of said n filters for treating an atmosphere outputfrom said at least one ink recovery reservoir; while at least a 2^(nd)valve selects a circulation pathway to said outlet face of a 2^(nd) oneof said filters: for some of the liquid outlet from said solventextraction means or from said solvent reservoir respectively, or forsome of the gas outlet from said solvent extraction means or from saidgas reservoir or from said 1^(st) one of said n filters respectively. 8.The device according to claim 5, comprising at least a circuit to bringsome of the gas outlet from said solvent extraction means, through theoutlet face of one of said n filter(s), said circuit carryingcirculation of this gas in a closed loop in a gas supply system of theprint head.
 9. The device according to claim 1, in which n>1, andcomprising: at least a 1^(st) valve to select one of said n filterstreating an atmosphere output from said at least one ink recoveryreservoir, or from said solvent extraction means respectively; and atleast a 2^(nd) valve to simultaneously clean another one of said nfilters.
 10. A supply circuit for at least one print head, comprising:at least one ink recovery reservoir, to recover ink not used forprinting and to supply said at least one print head; a recovery deviceof an atmosphere originating from said at least one ink recoveryreservoir, according to claim
 1. 11. A printer comprising at least oneprint head and a supply circuit according to claim 10, said print headcomprising a plurality of nozzles to form k jets, where k>1.
 12. Amethod for recovery of an atmosphere from at least one ink recoveryreservoir of a print machine comprising: filtering of an atmosphere fromsaid at least one ink recovery reservoir using at least one filtercomprising an inlet face, an outlet face and a filter body between saidinlet face and said outlet face, said filter being arranged: downstreamfrom said at least one ink recovery reservoir but upstream from solventextraction means, an atmosphere from said at least one ink recoveryreservoir passing through said inlet face, and then through said filterbody and through said outlet face, before being sent to said solventextraction means, or downstream from solvent extraction means, anatmosphere from said solvent extraction means passing through said inletface, and then through said filter body and through said outlet face,before being sent to at least one print head of said print machine,recovery of at least part of a liquid condensed on the surface of saidinlet face of said filter, before this liquid has passed through thesurface of the inlet face of the filter.
 13. The method according toclaim 12, in which the following are introduced through said output faceof said at least one filter: some of the liquid outlet from said solventextraction means or from a solvent reservoir respectively; and thenpossibly part of the gas that exits from said solvent extraction meansor from a gas reservoir, or respectively from another filter or from agas reservoir.
 14. The method according to claim 13, comprising nfilters, n>1, and in which a circulation pathway is selected to only oneof said n filters: for part of the liquid outlet from said solventextraction means or from a solvent reservoir respectively, or for someof the gas outlet from said solvent extraction means, or from a gasreservoir or from another filter respectively.
 15. The method accordingto claim 14, in which: a 1^(st) one of said n filters is selected tofilter an atmosphere from said at least one ink recovery reservoir, anda pathway to a 2^(nd) one of said n filters is selected for circulationof some of the liquid outlet from said solvent extraction means or fromsaid solvent reservoir respectively, or some of the gas outlet from saidsolvent extraction means, or from another filter respectively.
 16. Themethod according to claim 13, in which part of the gas output from saidsolvent extraction means circulates in a closed loop in a gas supplysystem of said print head.
 17. The method according to claim 12,comprising n filters, n>1, and in which an atmosphere from said at leastone ink recovery reservoir is filtered by a 1^(st) filter of said nfilters, a 2^(nd) filter of said n filters being cleaned at the sametime.
 18. The method according to claim 12, in which at least part ofthe liquid condensed on said inlet face of said at least one filterflows by gravity from said inlet face of said at least one filter and ispossibly directed to a reservoir.
 19. The method according to claim 12,in which at least part of the liquid condensed on said inlet face ofsaid at least one filter flows by gravity from said inlet face of saidat least one filter to a reservoir and is recovered firstly by aliquid - gas separator placed between said at least one filter and saidreservoir.
 20. The method according to claim 12, in which a flow of saidfiltered atmosphere is between 10 I/h and 10000 I/h.
 21. A device forrecovery of an atmosphere containing solvent vapours from at least oneink recovery reservoir of a print machine comprising: at least onefilter arranged downstream from said at least one ink recoveryreservoir, each filter comprising: comprising an inlet face, an outletface and a filter body between these two faces, at least a duct torecover at least part of a liquid condensed on the surface of said inletface of said at least one filter, before this liquid has passed throughthe surface of the inlet face of the filter, and each of said filterbeing : either upstream from a solvent condenser, an atmosphere fromsaid at least one ink recovery reservoir, passing through said inletface, and then through said at least one filter body and through saidoutlet face before being sent to said solvent condenser, or downstreamfrom a solvent condenser, an atmosphere from said solvent condenserpassing through said inlet face, and then through said filter body andthrough said outlet face before being sent to at least one print head ofthe print machine, respectively.